Recent catastrophic oil spills like the Deepwater Horizon (2010, 210 million gallons), first Gulf War (1990, 420 million gallons), Exxon Valdez (1989, 11 million gallons), and IXTOC 1 (1979, 140 million gallons) are major environmental threats. Significant damage to the marine ecosystem is visible in the form of dead sea-birds, otters, sea-turtles, marine mammals, contaminated planktons, and affected corals. Additionally, oil in bilge water, industrial oil spills from facility repairs, and daily normal operation are constant sources of pollution. Another potential environmental hazard comes from waste waters produced via fracking. Modern extraction techniques like directional drilling and hydraulic fracking are frequently used to access natural gas trapped in shale reserves. The hydrocarbon mixed water associated with shale gas-extraction significantly affects contaminant level in nearby wells and aquifers. The long-term detrimental impact of different oil contaminations on the food-chain is a huge concern. To mitigate the harmful environmental effect of fast spreading oil spills, rapid removal of oil from the water surface is important. Different oil spill cleanup techniques like physical sorption via porous sorbents, mechanical recovery with skimmers, in situ burning, dispersant mediated physical diffusion, and biodegradation have been used to this effect. However, the dynamic state of oil spill in the ocean waters, cost, and time are potential challenges to the existing cleanup methods. Further, some methods like the dispersants and floating booms made from nonrenewable materials pose additional burden to the environment. These limitations inspired the recent scientific impetus to develop new nanomaterials for efficient oil removal.
For example, magnetic nanocomposites were designed to address the difficulty in collection of conventional activated carbon adsorbents. Polysiloxane coated Fe2O3@C core-shell nanoparticles (NPs) were used for enhanced selectivity in oil-water separation. In a recently reported iron oxide-collagen nanobiocomposite, collagen from industrial wastes served as an oil absorbing agent and the iron oxide core provided magnetic actuation. Calcagnile et. al. incorporated weakly bound iron oxide NPs into a polyurethane foam modified with a hydrophobic polytetrafluoroethylene surface to facilitate oil absorption. Magnetite nanofillers infused in low epoxidized natural rubber showed high absorption capacity for petrol oil. A high concentration of iron oxide NPs within an alky resin biopolymer increased the oil absorption capacity of the composite. These studies highlight the potential of iron oxide NPs for oil removal. This is particularly attractive because iron oxide NPs are widely used in bio-applications and are known for low toxicity owing to the chemically stable oxide coating.
However, most studies were based on homogeneous oil samples and the hydrophobic materials would be unsuitable for submerged oil and are often toxic. Recently, polyacrylic acid-polystyrene co-polymer encapsulated, amphiphilic iron oxide NPs were designed for treatment of crude oil to address these limitations. The iron oxide NPs in most of these studies were synthesized under complex high-temperature and airless conditions, requiring complex, expensive and environmentally burdensome protocols. Additional ligand exchange steps were required to render the hydrophobic NPs biocompatible.
To minimize environmental impact and facilitate an easy scale-up for oil remediation applications, a facile synthetic route is required to directly generate stable, water soluble iron oxide NPs.